Technical Field
The present invention relates to a coordination method between access points using unlicensed frequency bands, which belongs to the field of wireless communication technologies.
Related Art
In recent years, with development of wireless communication technologies and popularization of intelligent terminals, mobile user demand for data communication has increased substantially, and expensive licensed frequency bands with limited bandwidth cannot meet the user demand. In order to release the pressure on mobile networks on licensed frequency bands, it is a new idea to cope with the challenge of high data amount by using unlicensed frequency bands with relatively rich resources. In addition to WiFi systems that have been massively deployed, various mobile operators and equipment manufacturers are seeking more technologies that use unlicensed frequency bands to carry data traffic of more mobile services. For example, LTE is deployed to unlicensed frequency bands, and a LTE air interface protocol is employed on the unlicensed frequency bands for communication, that is, LTE Advanced in Unlicensed Spectrums, abbreviated as LTE-U.
Development of the new technology that uses unlicensed frequency bands is faced with many challenges, in which fair coexistence with the existing WiFi systems is a primary issue. Employing a listen-before-talk (LBT) mechanism similar to WiFi and a discontinuous Transmission (DTX) mechanism is an effective method of sharing unlicensed spectrums. Any device using unlicensed frequency bands has to first monitor whether a channel is occupied before sending data. If the channel is idle in a certain period of time (e.g., within the backoff time randomly selected from a contention window), the device can occupy the channel and start transmission, but the channel occupation time cannot exceed certain limitations. At present, much standardized work is studying the LB T mechanism and the DTX mechanism of LTE-U.
As it is necessary to send data by channel competition on the unlicensed frequency bands and the continuous transmission time cannot exceed certain limitations, how the user quality of service (QoS) is ensured is also a problem to be urgently solved. In order to improve the user QoS, access points using unlicensed frequency bands need to adjust transmission parameters, for example, the size of the contention window or transmission idle time is reduced, so as to access a channel with higher probability to send data. However, this will definitely affect fairness of channel occupation of neighbor access points using the unlicensed frequency bands.
The existing solution of fair coexistence between access points using unlicensed frequency bands is mainly directed to optimization of LBT parameters and discontinuous transmission parameters of a single access point, which does not involve jointly adjusting parameters by multiple access points in the same network. For example, in a 3GPP standard proposal, it is proposed that a LTE-U base station can change channel access priority by adjusting LBT parameters, and in order to ensure fair coexistence with other access points, a LTE-U base station using a smaller contention window needs to reduce the maximum channel occupancy time. The proposal is directed to adjustment of LBT parameters in a single LTE-U base station, but does not involve coordination between LTE-U base stations. Therefore, this LBT parameter adjustment method of a single LTE-U base station cannot ensure fair coexistence with access points of another network.